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"I would never die for my beliefs because I might be wrong."

-- Bertrand Russell


Dec
1
comment What's with the very slightly larger mass of the neutron compared to the proton?
Sadly, they can not yet differentiate between proton and neutron. But it's a great achievement nonetheless.
Dec
1
comment What is an analog to QM's Hilbert space in GR?
You are really obsessed with this perfect fluid history, aren't you? I'm sorry but I can't tell you, that's outside of my expertise. It seems to me you should talk to some astrophysicist doing simulations of things like galaxies. That's typically the kind of field where people worry about such questions. Try to ask a question which has this explicitly in the topic title, maybe you'll get an expert to reply. +1 for Marek, exactly my thought. ;)
Dec
1
comment What is an analog to QM's Hilbert space in GR?
Depends how smooth you want it. Generally, for the equations to make sense, you only need existance of the second derivative. But I guess stronger assumptions of smoothness are made depending on what problems one wants to tackle.
Dec
1
revised What is an analog to QM's Hilbert space in GR?
added 162 characters in body
Dec
1
comment What is an analog to QM's Hilbert space in GR?
No, it's not a typo, but I admit I have not been clear enough. $N$ is the amount of particles you want to describe. You multiply by 6 because each particle has 3 spatial coordinates and 3 momenta along each spatial direction. The structure of phase space is that of a symplectic manifold.
Dec
1
answered What is an analog to QM's Hilbert space in GR?
Nov
30
comment Is there a conserved quantity that enforces planar orbits in central force motion?
Wait, isn't that precisely the angular momentum? You just said angular momentum has to be constant before that, so I assumed you already figured it out. I do know there is a Laplace-Runge-Lenz vector, but if I remember correctly, that one is associated to the ellipticity of the trajectory.
Nov
30
comment Why is the mapped universe shaped like an hourglass?
Actually, filtering the radiation of the galaxy from the CMB is a difficult task. Look at these images from COBE. Look at the equivalent picture but now taken by WMAP. You see there's always a red horizontal band in the middle. That's the galaxy, and they have to filter it out somehow.
Nov
30
answered Why is the mapped universe shaped like an hourglass?
Nov
30
comment How far does a trampoline vertically deform based on the mass of the object?
To be fair, the OP really asks about dynamics. But I agree that starting with explaining the static case can not hurt.
Nov
29
revised Reciprocal Lattices
deleted 64 characters in body
Nov
29
answered Reciprocal Lattices
Nov
29
answered Why is Physics so hard?
Nov
28
comment Searching books and papers with equations
@Lagerbaer, not a bad suggestion, but the problem is that there are so many idiosyncratic notations that you might miss what you are looking for just because someone wants to write his derivatives in "Newtonian fluxions" style instead of Leibniz notation or whatever. And just the problem of different names for the relevant variables is daunting enough.
Nov
28
comment Searching books and papers with equations
On the other hand, for integer sequences, there is a nice website cataloguing them: oeis.org . I wish someone would think up something like that for formula's. Maybe I should think about it.
Nov
28
comment Searching books and papers with equations
Nice question. Honestly, I don't know how to do it either. I just try to associate keywords I think are relevant. And I just play around until I find what I need. Or not. But one thing is certain, the search can be interesting in itself. Sometimes, I wasn't able to find out what I needed, but I still harvested all kinds of interesting articles.
Nov
28
revised Measuring the speed of light and defining the metre - absolute or relative?
added 19 characters in body
Nov
28
answered Measuring the speed of light and defining the metre - absolute or relative?
Nov
28
comment Is there a theory about kinetic energy “particles”?
When you bombard electrons with photons, you are in effect giving them kinetic energy. All particles are "kinetic energy particles". There's no need for an extra kind of particles. A change in kinetic energy corresponds to work being exerted by or on the system.
Nov
28
comment Four-dimensionalism vs energy economy
Never heard of it. Unless it means: the universe can be described as a 4-dimensional manifold, then it is a part of for instance GR or quantum field theory, but in and of itself, it is not rich enough to constitute a physical theory.